VARIATIONS IN THE COMPOSITION OF THE MILK. 375 



butyrine, caprine, caproine, and capriline. The margarine and oleine are principles found 

 in the fat throughout the body ; but the last-named substances are peculiar to the milk. 

 These are especially liable to acidification, and the acids resulting from their decomposi- 

 tion give the peculiar odor and flavor to rancid butter. 



Sugar of milk, sometimes called lactine, or lactose, is the most abundant of the solid 

 constituents of the mammary secretion. It is this principle that gives to the milk its 

 peculiar sweetish taste, although this variety of sugar is much less sweet than cane-sugar. 

 The chief peculiarities of milk-sugar are that it readily undergoes change into lactic acid 

 in the presence of nitrogenized ferments and takes on alcoholic fermentation slowly and 

 with difficulty. At one time, indeed, it was supposed that milk-sugar could not be de- 

 composed into alcohol and carbonic acid ; but it is now well established that this change 

 can be induced, the only peculiarity being that it takes place very slowly. In some parts 

 of the world, intoxicating drinks are made by the alcoholic fermentation of milk. 



A consideration of the nutritive action of the fatty and saccharine constituents of milk 

 belongs properly to the subjects of alimentation and nutrition. It may be stated here, 

 however, that these principles seem to be as necessary to the nutrition of the child as the 

 nitrogenized principles ; although the precise manner in which they affect the develop- 

 ment and regeneration of the tissues has not been ascertained. 



Inorganic Constituents of Milk. It is probable that many inorganic principles exist 

 in the milk which are not given in the table ; and the separation of these principles from 

 their combinations with organic matters is one of the most difficult problems in physio- 

 logical chemistry. This must be the case for, during the first months of extra-uterine 

 existence, the child derives all the inorganic, as well as the organic matters necessary to 

 nutrition and development, from the breast of the mother. The reaction of the milk 

 depends upon the presence of the alkaline carbonates, and these principles are important 

 in preserving the fluidity of the caseine. It is not determined precisely in what form iron. 

 exists in the milk, but its presence here is undoubted. A comparison of the composition 

 of the milk with that of the blood shows that most of the important inorganic prin- 

 ciples found in the latter fluid exist also in the milk. 



Hoppe has indicated the presence of carbonic acid, nitrogen, and oxygen, in solution 

 in milk. Of these gases, carbonic acid is the most abundant. It is well known that 

 the presence of gases in solution in liquids renders them more agreeable to the taste, 

 and carbonic acid increases very materially their solvent properties. Aside from these 

 considerations, the precise function of the gaseous constituents of the milk is not ap- 

 parent. 



A study of the composition of the milk fully confirms the fact, which we have already 

 had occasion to state, that this is a typical alimentary fluid and presents in itself the 

 proper proportion and variety of material for the nourishment of the body during the 

 period when the development of the system is going on with its maximum of activity. 

 The form in which its different nutritive constituents exist is such that they are easily 

 digested and are assimilated with great rapidity. 



Variations in the Composition of the Milk. 



Vernois and Becquerel have indicated a certain amount of variation at different ages 

 and at different periods in lactation, but they show, at the same time, that the fluid is not 

 subject to changes in its composition sufficiently great to influence materially the nutrition 

 of the child. 



If the composition of the milk be compared at different periods of lactation, it will be 

 found to undergo great changes during the first few days. In fact, the first fluid secreted 

 after parturition is so different from ordinary milk, that it has been called by another name. 

 It is then known as colostrum, the peculiar properties of which will be considered more 

 fully hereafter, under a distinct head. As the secretion of milk becomes established, the 

 fluid, from the first to the fifteenth day, becomes gradually diminished in density and 



